Photonic crystals (PCs) are a class of structure engineered materials that prohibit propagation of light modes of certain frequencies. Photonic crystal waveguides (PCWGs) are linear defects made in PCs that can propagate photonic modes at frequencies prohibited in bulk PCs. As a result, the electromagnetic field is tightly confined within the waveguides cross-section. This enables sharp bends and low-loss sharp splitters with low mode volumes inaccessible for conventional waveguides. PCWGs may also be engineered for a particular dispersion (e.g., a very low group velocity, a negative group velocity, or a rapidly changing group velocity.) These properties may be useful for the development of electro-optical integrated circuits.
A common type of PCWG is a quasi two-dimensional waveguide. A quasi two-dimensional waveguide is fabricated in a slab of optically transparent material and has essentially two dimensional patterns. Such structures are relatively easy to fabricate, however, light can be lost into the cladding above and below the waveguide. In the third dimension, the light is essentially index guided. Therefore, the index of refraction in both claddings should be as low as possible. The top cladding may be air with an index of refraction equal to one, which sets an upper limit for the parameter space available for designing low loss waveguides. If, however, the bottom cladding has an index of refraction greater than one, the parameter space will be limited by this index of refraction.
For these and other reasons, there is a need for the present invention.